The HHL algorithm[1]} consists of three steps, which are QPE[2]}, [3]}, [4]}, \(R(\lambda ^{-1})\) -rotation, and inverse QPE.
The schematic quantum circuit of the HHL algorithm is plotted in Fig. 3.
These three steps were experimentally and explicitly realized in Ref. [5]}In Fig. 1 of Ref. [5]} the rotations \(R_y (\pi / 2^r)\)  and \(R_y (2 \pi / 2^r)\)  should be interchanged. by selecting a linear equation \(A {\mathbf {x}} = {\mathbf {b}}\) , where
\(A = \frac{1}{2} \left( \begin{array}{cc}3 & 1 \\1 & 3\end{array} \right) \hspace{28.45274pt}{\mathbf {b}} = \left( \begin{array}{c}b_0 \\ b_1\end{array} \right)\) 
